146
Alternative Fuels for Transportation
Retarding the start of injection causes injection to begin when combustion
chamber pressures and temperatures are higher, thus shortening the ignition
delay. However, shortening the ignition delay increases the amount of diffusion combustion, with a consequent increase in CO and smoke emissions.
Since the effect of ignition delay on NO x emissions is opposite the effect on
CO and smoke, choice of the desired ignition delay is a compromise.
As previously mentioned, when used as the complete fuel, ethanol will
not self-ignite in an ordinary CI engine. However, there are a number of
techniques available to use ethanol fuel in a CI engine. These techniques
can be grouped into those involving modification or adaptation of the
engine to be able to combust ethanol and those that rely on the fuel being
modified to achieve CI engine compatibility, including blending of ethanol
with diesel fuel. The most common methods for achieving dual fuel operation are
1. Alcohol fumigation: The addition of alcohols to the intake air charge,
displacing up to 50% of the diesel fuel demand.
2. Dual injection: Separate injection systems for each fuel, displacing
up to 90% of diesel fuel demand.
3. Alcohol-diesel fuel blend: Mixture of the fuels just prior to injection,
displacing up to 25% of the diesel fuel demand.
4. Alcohol-diesel fuel emulsion: Using an emulsifier to mix the fuels to
prevent separation, displacing up to 25% diesel fuel demand.
5.5.1 Fumigation
Fumigation is a method by which alcohol is introduced into the engine by
carbureting, vaporizing, or injecting the alcohol into the intake air stream.
This requires the addition of a carburetor, vaporizer or injector, along with a
separate fuel tank, lines, and controls.
The intake manifold and intake valves of a conventional CI engine handle
only air but, in a technique known as fumigation, ethanol can be blended
with the air to supply partial fueling to the engine, while the primary fuel
of adequate cetane rating is injected through the usual fuel injection system.
While carburetors have been investigated as an inexpensive way of introducing ethanol into the intake airstream (Ajav, Singh, and Bhattacharya 1998;
Goering and Wood 1982), manifold injection is regarded as the preferred
approach in keeping with gasoline injection systems used in most applications at present.
Sullivan and Bashford (1981) sprayed ethanol into the air inlet of a turbocharged CI engine. Impingement of the ethanol on the compressor blades
caused blade erosion after only 30 hours of running. Injection of the ethanol
separately into each engine cylinder is preferable to insure equal distribution
of the ethanol to each cylinder. Otherwise, the maximum rate of fumigation
Alternative Fuels for Transportation
Retarding the start of injection causes injection to begin when combustion
chamber pressures and temperatures are higher, thus shortening the ignition
delay. However, shortening the ignition delay increases the amount of diffusion combustion, with a consequent increase in CO and smoke emissions.
Since the effect of ignition delay on NO x emissions is opposite the effect on
CO and smoke, choice of the desired ignition delay is a compromise.
As previously mentioned, when used as the complete fuel, ethanol will
not self-ignite in an ordinary CI engine. However, there are a number of
techniques available to use ethanol fuel in a CI engine. These techniques
can be grouped into those involving modification or adaptation of the
engine to be able to combust ethanol and those that rely on the fuel being
modified to achieve CI engine compatibility, including blending of ethanol
with diesel fuel. The most common methods for achieving dual fuel operation are
1. Alcohol fumigation: The addition of alcohols to the intake air charge,
displacing up to 50% of the diesel fuel demand.
2. Dual injection: Separate injection systems for each fuel, displacing
up to 90% of diesel fuel demand.
3. Alcohol-diesel fuel blend: Mixture of the fuels just prior to injection,
displacing up to 25% of the diesel fuel demand.
4. Alcohol-diesel fuel emulsion: Using an emulsifier to mix the fuels to
prevent separation, displacing up to 25% diesel fuel demand.
5.5.1 Fumigation
Fumigation is a method by which alcohol is introduced into the engine by
carbureting, vaporizing, or injecting the alcohol into the intake air stream.
This requires the addition of a carburetor, vaporizer or injector, along with a
separate fuel tank, lines, and controls.
The intake manifold and intake valves of a conventional CI engine handle
only air but, in a technique known as fumigation, ethanol can be blended
with the air to supply partial fueling to the engine, while the primary fuel
of adequate cetane rating is injected through the usual fuel injection system.
While carburetors have been investigated as an inexpensive way of introducing ethanol into the intake airstream (Ajav, Singh, and Bhattacharya 1998;
Goering and Wood 1982), manifold injection is regarded as the preferred
approach in keeping with gasoline injection systems used in most applications at present.
Sullivan and Bashford (1981) sprayed ethanol into the air inlet of a turbocharged CI engine. Impingement of the ethanol on the compressor blades
caused blade erosion after only 30 hours of running. Injection of the ethanol
separately into each engine cylinder is preferable to insure equal distribution
of the ethanol to each cylinder. Otherwise, the maximum rate of fumigation